Method for predicting creep property of ODS steel under high-temperature and high-irradiation conditions

Abstract

The invention relates to a method for predicting creep properties of oxide dispersion strengthened (ODS) steel under high-temperature and high-irradiation conditions. A complex crystal plasticity constitutive model is developed and used for accurately predicting the performance of the ODS steel in the aspects of irradiation hardening and creep behaviors, and the model incorporates space distribution of holes and oxides. The developed model is highly matched with experimental data under different temperatures and irradiation doses, and shows strong robustness. Along with the increase of the irradiation dose, the yield stress of the irradiated ODS steel is also increased. The yield strength of the ODS steel and the irradiation dose are in a linear relation, and the yield strength is increased along with the increase of the irradiation dose at first and then decreased. The cavity size is stably increased, and the cavity spacing is increased after the initial reduction. Therefore, the cavity hardening effect is gradually weakened after the initial enhancement. On the contrary, along with the rise of the irradiation temperature, the yield strength is reduced, which is caused by the enlargement of the void spacing at a higher temperature. And the nonlinear correlation between the creep rate of the irradiated ODS steel and the irradiation dose is obtained. The creep property of the ODS steel irradiated at a low dosage or a high dosage is relatively poor, and the ODS steel shows a high creep rate under low applied stress. On the contrary, under the medium dosage, due to the fact that the number of irradiation holes is small and the strength of oxide particles is high, the creep property is better. And the spherical void shows better creep resistance, and the influence of void spacing on the creep performance is more obvious than that of void size. Under low dosage and high dosage, the creep property is reduced along with the rise of irradiation temperature, and in addition, under lower dosage, the influence of the irradiation temperature on the creep property is not obvious as under higher dosage. The invention provides an efficient theoretical method for accurately evaluating the irradiation performance of the ODS steel in a complex environment.

Description

Technical Field

[0001] The present invention relates to the field of creep performance prediction under high temperature and high irradiation environment, and specifically to a crystal plasticity model, a theory of void hardening caused by irradiation, an oxide dispersion strengthening theory and a creep rate calculation model related to threshold stress. A hardening and creep theoretical model with unified parameters is established to realize accurate prediction of the creep performance of oxide dispersion strengthened (ODS) steel under different irradiation doses and irradiation temperatures. Background Art

[0002] Generation IV fission reactors need to operate in an environment with high coolant temperatures, high neutron fluxes, and long-term high creep loads. Therefore, they require structural materials with excellent mechanical properties, thermal stability, and long-term creep performance. Oxide dispersion strengthened (ODS) steels are strong contenders for Generation IV reactors due to their excellent mechanical strength, remarkable microstructural stability at high temperatures, and resistance to creep deformation. The high density of oxide particles in the matrix plays a key role in imparting these extraordinary properties. Through effective dislocations and grain boundaries, these fine particles help stabilize the structure and enhance the overall strength of the material.

[0003] Both neutron irradiation and ion implantation are experimental techniques used to evaluate the radiation resistance of ODS steels. Ion implantation offers several advantages, including lower cost, shorter irradiation times, and the ability to provide non-radioactive samples for post-implantation examination in standard preparation laboratories. This has led to a large number of studies on ODS steels utilizing ion implantation. ODS alloys containing 0.5% Y2O3 were irradiated with neutrons up to 16.2 dPa at temperatures of 250°C, 350°C, and 450°C. The level and characteristics of the radiation damage observed were found to be significantly affected by the irradiation temperature and the distribution of the ODS particles. A zirconium-doped nanocrystalline 14YWTZ ODS steel consisting of a ferrite matrix with an average grain size of 50 nm and a high density of oxide nanoprecipitates with an average diameter of 3.3 nm. The ODS steel has approximately 3×10 16 m -2 The unusually high sink strength of Y2TiO5 is mainly due to the presence of grain boundaries. The combination of grain boundaries (GBs) with Y2TiO5 was found to significantly enhance the aggregation of helium bubbles. This is because GBs can act as effective defect sinks and diffusion pathways, while Y2TiO5 has a strong ability to trap helium atoms. Although ODS steels are well known for their favorable properties, there are also reports that ODS steels with lower oxide particle density may exhibit higher levels of radiation hardening and transform to a brittle-ductile state after low-temperature irradiation compared to conventional RAFM steels.

[0004] The invention analyzes the radiation hardening and creep behaviors of ODS steel at high temperature and dosage, analyzes the influence of temperature and dosage on the radiation hardening and creep rate, and discusses the creep mechanism of ODS steel. Summary of the invention

[0005] The present invention is based on experimental data combined with consideration of radiation-induced void evolution and oxide particle evolution, and establishes a unified parameterized hardening and creep model through a crystal plasticity model and a creep rate analysis model related to threshold stress; combined with the spatial distribution of voids and oxides, the model is used to accurately predict the radiation hardening and creep behavior of ODS steel, and to achieve quantitative analysis of creep rates under different radiation doses and different radiation temperatures. At the same time, by adjusting the radiation dose and radiation temperature, the creep rate and threshold stress of ODS steel under specific conditions are obtained, and design guidance for ODS steel is achieved.

[0006] The technical solution of the present invention is:

[0007] Determine the material parameters of the ODS steel used, including the relevant parameters of the element physical parameters. The materials used in the present invention are ODS steels with contents of 14.9Cr-1.92W-0.34Y2O3 (wt%) and 14Cr-3W-0.3Y2O3 (wt%), and predict the performance of other ODS steels. The void / helium bubble sizes in ODS steels under different irradiation environments are shown in the following table:

[0008] Table 1 Parameters of helium bubbles in 15Cr-ODS steel and 15Cr-ODS steel matrix after irradiation.

[0009]

[0010] Table 2 Void parameters in ODS steel at different irradiation doses.

[0011]

[0012] Table 3 Parameters of oxide particles in ODS steel at different irradiation doses.

[0013] Table 4 Void parameters in ODS steel at different irradiation temperatures.

[0014]

[0015] In classical crystal plasticity theory, the deformation of a crystal is described by deformation gradient and velocity gradient:

[0016] F=F e ·F p

[0017]

[0018] in "e" and "p" represent the elastic and plastic parts respectively. represents the deformation gradient. Plastic deformation is mainly caused by dislocation slip, so the plastic part of the velocity gradient is composed of the cumulative shear rate of the twelve slip systems:

[0019]

[0020] Among them, N s is the total number of slip systems. is the Schmid factor, s a represents the dislocation slip direction, n a represents the normal direction of dislocation slip. is the reference plastic strain rate, m represents the strain rate sensitivity coefficient, τ a =σ:R a represents the local shear stress and σ is the Cauchy stress. is the critical partial shear stress. The defects induced under high temperature and strong radiation are mainly considered as voids.

[0021] Therefore, the critical partial shear stress is expressed as

[0022]

[0023] in It is solid solution strengthening. is dislocation strengthening, It is grain strengthening. It is hollow reinforcement. It is oxide dispersion strengthening. The self-consistent plasticity method is used to characterize the stress-strain relationship of polycrystalline materials by considering the interaction and behavior of individual grains.

[0024] Solid solution structure, dislocations, grain size, voids and oxide particles have a strengthening effect on the mechanical properties of materials by hindering dislocation movement. Solid solution strengthening is expressed as

[0025]

[0026] where k i represents the hardening coefficient, X i is the atomic content, for substitutional solid solution Z = 3 / 4, k Cr =9.95MPa / at% 3 / 4 and k W =75.79MPa / at% 3 / 4 , m is the Taylor factor. Dislocation strengthening is expressed as

[0027]

[0028] where h nis the dislocation strengthening coefficient. As the plastic strain increases, the Mecking and Kocks model captures the change in dislocation density due to proliferation and annihilation.

[0029]

[0030] in represents the reference plastic shear rate, k1 is the multiplication factor, is the annihilation coefficient, and the relationship between the two coefficients is

[0031]

[0032] in is the loading strain rate, is the reference strain rate, D α is the drag stress, g α is the normalized activation energy, k is the Boltzmann constant, and χ is the interaction parameter. Grain strengthening is expressed as

[0033]

[0034] where k hp is the Hall-Petch coefficient, k hp =0.2Gb 1 / 2 , d is the average grain size. The effectiveness of voids in hindering dislocations is closely related to their shape. The critical partial shear stress of a spherical void is expressed as

[0035]

[0036] Where L is the hole spacing, is the harmonic mean size, D is the void diameter and Ψ is the fitting coefficient. For cubic voids, the cross-sectional shapes of dislocations and voids are different. The cross-sectional shapes include triangles and hexagons. The overall contribution of voids to the critical partial shear stress is expressed as

[0037]

[0038] The hindering effect of the triangular cross section is expressed as The barrier effect of the hexagonal interface is Oxide particles also strengthen the mechanical properties of materials by hindering dislocation movement. The main mechanism of oxide particle strengthening is the cutting strengthening mechanism τ cutting 、Orowan bypasses the reinforcement mechanism τ orowan and the climbing mechanism τ climb Their expressions are

[0039]

[0040] τ=min(τ climb ,τ orowan ,τ cutting )

[0041] Among them, A and B are constant parameters, D is the spatial particle diameter, L is the particle distance, r a is the dislocation core radius, assumed to be the magnitude of the Burgers vector. ε is the misfit strain, calculated as ε = b / 4r, where r is the radius of the oxide particle, which can be obtained experimentally. τ represents the minimum stress for the three interaction mechanisms. This assumption does not accurately reflect the physical model. Although the slip plane of the dislocation remains fixed in the matrix, the precipitates are randomly distributed. In addition, even particles of the same size will exhibit different dislocation bypassing mechanisms. Therefore, the critical partial shear stress contribution of the spatially distributed probabilistic model is expressed as:

[0042]

[0043] in and represent the mechanisms of climb strengthening, shear strengthening, and bypass strengthening, respectively. Therefore, a refined model of oxide particle strengthening is established by integrating the probabilistic nature and spatial distribution of the interaction between dislocations and particles. This new approach accounts for the random distribution of precipitates and the different mechanisms by which dislocations bypass particles of the same size. Therefore, the critical partial shear stress contribution is expressed as

[0044] The coupled threshold stress can be regarded as the coupled creep resistance of voids and oxide particles under irradiation. The unified creep rate equation considering the irradiation-induced void evolution theory and oxide diffusion strengthening theory is expressed as:

[0045]

[0046] τ L is the dislocation line tension, τ L =Gb 2 . G is the shear modulus, G = 84-16 / (e 448 / T -1), b is the Burgers vector. L is the strain hardening parameter, σ app is the applied stress, σ D is the threshold stress, α is an empirical constant. N is the stress- and temperature-dependent dislocation mobility, described by the following equation:

[0047]

[0048] D osd represents the pre-exponential factor, k B is the Boltzmann constant, Q sd represents the activation energy of self-diffusion, Rg is the gas constant, R m represents the tensile strength at room temperature. The threshold stress is related to the intrinsic properties of voids and oxide particles, showing their effectiveness in blocking dislocation motion, and can be expressed as

[0049]

[0050] Finally, the calculation results are processed and analyzed to obtain a comparison between the model and the experimental data, and to predict the creep rate at different irradiation doses and temperatures.

[0051] Beneficial Effects

[0052] A complex crystal plasticity constitutive model was developed to accurately predict the radiation hardening and creep behavior of ODS steels, which incorporates the spatial distribution of voids and oxides. The developed model showed good agreement with experimental data at different temperatures and irradiation doses, demonstrating its strong robustness. The yield stress of irradiated ODS steels increased with increasing irradiation dose. The yield strength of ODS steels showed a linear relationship with irradiation dose, initially increasing with increasing irradiation dose and then decreasing. The void size grew steadily, while the void spacing increased after an initial decrease. Therefore, the void hardening effect gradually weakened after an initial increase. In contrast, the yield strength decreased with increasing irradiation temperature, which was caused by the expansion of void spacing at higher temperatures. Nonlinear dependence of creep rate of irradiated ODS steels on irradiation dose. ODS steels irradiated at low or high doses showed relatively poor creep performance and exhibited higher creep rates at low applied stresses. In contrast, at medium doses, the creep performance was better due to the small number of irradiated voids and high strength of oxide particles. Spherical voids show better creep resistance, and the effect of void spacing on creep performance is more significant than that of void size. At low and high doses, creep performance decreases with increasing irradiation temperature. In addition, at lower doses, the effect of irradiation temperature on creep performance is not as obvious as at higher doses. This work provides an efficient theoretical method for accurately evaluating the irradiation performance of ODS steel in complex environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 (a) is the contribution of various strengthening mechanisms to the yield strength of ODS steel before and after irradiation, and (b) is the comparison between the irradiation yield strength increment calculated by the current model and the experimental results.

[0054] Figure 2 (a) is the curve of the variation of void and oxide particle diameter with radiation dose; (b) is the curve of the variation of void spacing and oxide particle density with radiation dose.

[0055] Figure 3 (a) How does the creep behavior of ODS steel change with the change of irradiation dose at 823K? (b) The effect of void spacing on the creep behavior of ODS steel is studied when the void spacing is 30 nm, 50 nm and 70 nm respectively under the condition of a constant void size of 5 nm? (c) The effect of void size on the creep behavior of ODS steel is studied when the void spacing is 50 nm, the diameters of spherical voids are 5 nm, 10 nm and 15 nm respectively, and the side lengths of cubic voids are 5 nm, 10 nm and 15 nm respectively.

[0056] Figure 4 It is the prediction of creep properties of ODS steel under different irradiation temperatures in 100dpa and 500dpa environments. DETAILED DESCRIPTION

[0057] Combined with the helium bubble data in Table 1 and the attached Figure 1 (a) The contribution of various strengthening mechanisms to the yield strength of ODS steel before and after irradiation and the Figure 1 (b) Comparison of the irradiation yield strength increment calculated by the current model with the experimental results. Using the crystal plasticity constitutive model, the yield strength change before and after irradiation is obtained by considering the solid solution structure, dislocations, grain size, oxides, and void / helium bubble strengthening mechanism. This is then compared with the experimental data to verify the robustness of the model.

[0058] To further explain its technical solution, the present invention is not limited to the following examples, and all design ideas utilizing the present invention fall within the protection scope of the present invention.

[0059] Oxide dispersion strengthening refers to adding a certain amount of thermodynamically stable oxides to high-temperature alloys, dispersing them in the matrix to form an oxide dispersion phase that is insoluble in the matrix; the new phase hinders dislocation movement in the alloy and strengthens the mechanical properties of the material. The evolution of irradiation-induced voids and oxide particle distribution will change with changes in irradiation and irradiation temperature. Based on microstructural data and theoretical models, the creep performance of materials in different irradiation environments can be predicted.

[0060] Specific steps: Collect ODS steel experimental data and obtain the material parameters involved in the method of the present invention as shown in Table 2.

[0061] Table 5. Material parameters.

[0062]

[0063] The robustness of the model was verified by comparing the model-calculated yield strength increment and the experimental yield strength increment of ODS steel at different irradiation temperatures. Then, the distribution evolution data of voids and oxide particles at different irradiation doses were collected to obtain the attached Figure 2 According to the attached Figure 2 , the threshold stress and creep rate curves of voids and oxide particles at 100-390dpa were obtained, and the creep performance prediction of ODS steel under different irradiation doses was realized (Appendix Figure 3 a). According to the law of void evolution, the influence of different void shapes, void diameters and void spacing on creep performance is explored (Appendix Figure 3 a, b) in order to control the microstructure and guide alloy design in the future. Collect the void data in ODS steel at different irradiation temperatures, obtain the threshold stress and creep rate change curves contributed by voids and oxide particles at different temperatures, and realize the creep performance prediction of ODS steel at different irradiation temperatures (Appendix Figure 4 ).

[0064] Therefore, the present invention has good accuracy in analyzing the creep rate of ODS steel under irradiation environment, and can effectively predict the creep resistance of the material under different irradiation doses and irradiation temperatures, providing a reliable theoretical model for analyzing the evolution of microscopic defects and creep resistance of ODS steel under irradiation environment.

Claims

1. A method for predicting creep properties of oxide dispersion strengthened (ODS) steel under high temperature and high irradiation environment, combining the crystal plasticity model, the radiation-induced void evolution theory, and the oxide dispersion strengthening theory and creep rate analysis model considering the size distribution and spatial distribution of oxide particles, characterized by: The strengthening effect of void evolution in ODS steel under high temperature and high irradiation environment is considered, including the changes in void size and shape. The voids in the material are generated when the matrix is ​​in an irradiation environment; dislocation, grain size, and solid solution strengthening are the hardening mechanisms of the material before irradiation. Through the crystal plasticity model and the creep rate analysis model related to the threshold stress, a unified parameterized hardening and creep model is established; combined with the spatial distribution of voids and oxides, the model can be used to accurately predict the radiation hardening and creep behavior of ODS steel, and realize the quantitative analysis of creep rate under different irradiation doses and different irradiation temperatures. At the same time, by adjusting the irradiation dose and irradiation temperature, the creep rate and threshold stress of ODS steel under specific conditions are obtained, and the design guidance of ODS steel is realized.

2. The method for predicting creep properties of ODS steel under high temperature and high radiation environment according to claim 1 is characterized in that The inherent parameters of the material and the existing experimental data are used to accurately calculate the creep rate and threshold stress of the involved void evolution, strength and creep rate models under different irradiation doses and temperatures.

3. According to the method of use according to any one of claims 1-2, the specific steps of the processing method are as follows: Determine the basic material parameters required in the model and collect relevant physical parameters of related materials. The coupled threshold stress can be regarded as the coupled creep resistance of voids and oxide particles under irradiation. The unified creep rate equation considering the irradiation-induced void evolution theory and oxide diffusion strengthening theory is expressed as: τ L is the dislocation line tension, τ L =Gb 2 . G is the shear modulus, G = 84-16 / (e 448 / T -1), b is the Burgers vector. L is the strain hardening parameter, σ app is the applied stress, σ D is the threshold stress, α is an empirical constant. N is the stress- and temperature-dependent dislocation mobility, described by the following equation: D osd represents the pre-exponential factor, k B is the Boltzmann constant, Q sd represents the activation energy of self-diffusion, R g is the gas constant, R m represents the tensile strength at room temperature. The threshold stress is related to the intrinsic properties of voids and oxide particles, showing their effectiveness in blocking dislocation motion, and can be expressed as Analyze and process theoretical calculation results.

4. The specific steps according to claim 3, characterized in that: Determine effective material parameters; the material used in the present invention is ODS steel with a content of 14.9Cr-1.92W-0.34Y2O3 (wt%) (15Cr-ODS) and 14Cr-3W-0.3Y2O3 (14Cr-ODS) (wt%), and performance prediction of other ODS steels.

5. According to claim 3, it is characterized in that: The effectiveness of voids in hindering dislocations is closely related to their shape. The critical partial shear stress of a spherical void is expressed as Where L is the hole spacing, is the harmonic mean size, D is the void diameter and Ψ is the fitting coefficient. For cubic voids, the cross-sectional shapes of dislocations and voids are different. The cross-sectional shapes include triangles and hexagons. The overall contribution of voids to the critical partial shear stress is expressed as The hindering effect of the triangular cross section is expressed as The barrier effect of the hexagonal interface is Oxide particles also strengthen the mechanical properties of materials by hindering dislocation movement. The main mechanism of oxide particle strengthening is the cutting strengthening mechanism τ cutting 、Orowan bypasses the reinforcement mechanism τ orowan and the climbing mechanism τ climb Their expressions are τ=min(τ climb ,t orowan ,t cutting ) Among them, A and B are constant parameters, D is the spatial particle diameter, L is the particle distance, r a is the dislocation core radius, assumed to be the magnitude of the Burgers vector. ε is the misfit strain, calculated as ε = b / 4r, where r is the radius of the oxide particle, which can be obtained experimentally. τ represents the minimum stress for the three interaction mechanisms. This assumption does not accurately reflect the physical model. Although the slip plane of the dislocation remains fixed in the matrix, the precipitates are randomly distributed. In addition, even particles of the same size will exhibit different dislocation bypassing mechanisms. Therefore, the critical partial shear stress contribution of the spatially distributed probabilistic model is expressed as: in and represent the mechanisms of climb strengthening, shear strengthening, and bypass strengthening, respectively. Therefore, a refined model of oxide particle strengthening is established by integrating the probabilistic nature and spatial distribution of the interaction between dislocations and particles. This new approach accounts for the random distribution of precipitates and the different mechanisms by which dislocations bypass particles of the same size. Therefore, the critical partial shear stress contribution is expressed as 6. According to claim 3, it is characterized in that the critical shear and stress are constructed in the framework of the crystal plasticity model and all known microstructural strengthening mechanisms are considered. In the classical crystal plasticity theory, the deformation of the crystal is described by the deformation gradient and the velocity gradient: F=F e ·F p in "e" and "p" represent the elastic and plastic parts respectively. represents the deformation gradient. Plastic deformation is mainly caused by dislocation slip, so the plastic part of the velocity gradient is composed of the cumulative shear rate of the twelve slip systems: Where N s is the total number of slip systems. is the Schmid factor, where s a represents the dislocation slip direction, n a represents the normal direction of dislocation slip. is the reference plastic strain rate, m represents the strain rate sensitivity coefficient, τ a =σ:R a represents the local shear stress and σ is the Cauchy stress. is the critical partial shear stress. The defects induced by high temperature and strong irradiation are mainly considered as voids. Therefore, the critical partial shear stress is expressed as in, It is solid solution strengthening. is dislocation strengthening, It is grain strengthening. It is hollow reinforcement. It is oxide dispersion strengthening. The self-consistent plasticity method is used to characterize the stress-strain relationship of polycrystalline materials by considering the interaction and behavior of individual grains. Solid solution structure, dislocations, grain size, voids and oxide particles have a strengthening effect on the mechanical properties of materials by hindering dislocation movement. Solid solution strengthening is expressed as where k i represents the hardening coefficient, X i is the atomic content, for substitutional solid solution Z = 3 / 4, k Cr =9.95MPa / at% 3 / 4 and k W =75.79MPa / at% 3 / 4 , M is the Taylor factor. Dislocation strengthening is expressed as Among them, h n is the dislocation strengthening coefficient. As the plastic strain increases, the Mecking and Kocks model captures the change in dislocation density due to proliferation and annihilation. in, represents the reference plastic shear rate, k1 is the multiplication factor, is the annihilation coefficient, and the relationship between the two coefficients is in, is the loading strain rate, is the reference strain rate, D α is the drag stress, g α is the normalized activation energy, k is the Boltzmann constant, and χ is the interaction parameter. Grain strengthening is expressed as Among them, k hp is the Hall-Petch coefficient, k hp =0.2Gb 1 / 2 , d is the average grain size.

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